Presence of plicidentine in the oral teeth of the coelacanth Latimeria chalumnae Smith 1939 (Sarcopterygii; Actinistia)

The extant coelacanth Latimeria is a sarcopterygian predatory fish with caniniform teeth on its upper and lower jaws. The teeth are constituted of a cone of dentine with an apical cap of enamel, and they are fixed to the osseous component of the jaws by an attachment bone. Internal walls of the tooth base show folds that have been firstly interpreted in the past as radial vascular canals. Three-dimensional visualisation of these foldings using X-ray tomographic techniques and new histological interpretation lead to reconsider these structures as true plicidentine. The folds of the dentine do not invade the whole pulp cavity of the tooth contrary to the plicated condition of most fossil sarcopterygian fishes (e.g., Eusthenopteron, Porolepis, Megalichthys) certain fossil marine reptiles (ichthyosaurs) and extant varanids; in Latimeria they are limited to the lower third to the half of the pulp cavity. The presence of plicidentine in Latimeria's teeth is proposed to be a plesiomorphic character for sarcopterygians.

Limb-bone histology of temnospondyls: implications for understanding the diversification of palaeoecologies and patterns of locomotion of Permo-Triassic tetrapods

The locomotion of early tetrapods has long been a subject of great interest in the evolutionary history of vertebrates. However, we still do not have a precise understanding of the evolutionary radiation of their locomotory strategies. We present here the first palaeohistological study based on theoretical biomechanical considerations among a highly diversified group of early tetrapods, the temnospondyls. Based on the quantification of microanatomical and histological parameters in the humerus and femur of nine genera, this multivariate analysis provides new insights concerning the adaptations of temnospondyls to their palaeoenvironments during the Early Permian, and clearly after the Permo-Triassic crisis. This study therefore presents a methodology that, if based on a bigger sample, could contribute towards a characterization of the behaviour of species during great evolutionary events.